The present invention relates generally to oil recovery, and more particularly to down hole separation of produced fluid in a well bore into gases and liquids.
Many oil production wells require artificial lift equipment to raise the produced oil to the surface well head after the oil enters the well bore from an adjacent fluid production zone penetrated by the well bore. However, the oil entering the well bore from the fluid production zone is typically contained within a produced fluid mixture having two phases, a gas phase and a liquid phase. The liquid phase includes the oil as well as water, while the gas phase includes dissolved or otherwise entrained gases and/or free gases. The artificial lift equipment is generally effective for raising the liquids to the surface, but conversely is relatively ineffective when produced fluid mixtures having a high gas content are encountered. Therefore, it is desirable to separate the produced fluid mixture into the gases and liquids before employing the artificial lift equipment to raise the liqulids to the surface.
The present invention recognizes the need for a gas-liquid separator positionable down hole in a well bore which effectively separates a produced fluid mixture into gases and liquids before utilizing artificial lift equipment to raise the liquids to the surface. Accordingly, it is an object of the present invention to provide such a gas-liquid separator and a method of operating the same. More particularly, it is an object of the present invention to provide an essentially static gas-liquid separator for centrifugally separating a produced fluid mixture into gases and liquids, including hydrocarbon liquids, down hole in a well bore before raising the liquids to the surface by means of an artificial lift assembly associated with the gas-liquid separator. These objects and others are accomplished in accordance with the invention described hereafter.
The present invention is a gas-liquid separator positionable down hole in a well bore. The gas-liquid separator comprises an external tube and an internal tube. The external tube has an external tube interior and an internal tube correspondingly has an internal tube interior. The internal tube is positioned in the external tube interior with the longitudinal axes of the internal and external tubes substantially aligned, thereby forming an internal annulus between the external tube and internal tube, which defines a free gas flowpath. The internal tube interior defines a reduced-gas fluid flowpath. The gas-liquid separator further comprises a plate having a start point and an end point. The plate at least partially encircles the external tube to form a curved flow channel, which defines a produced fluid mixture flowpath. A first internal annulus opening is provided in the external tube beyond the start point of the plate, which defines a free gas inlet port for the free gas flowpath. The external tube preferably has a flared portion positioned at or proximal to the first internal annulus opening which flares outwardly as the flared portion extends away from the start point of the plate. The first internal annulus opening preferably comprises a plurality of flared perforations extending through the flared portion of the external tube.
The internal tube extends from the external tube interior beyond the first internal annulus opening and an internal tube interior opening is provided in the internal tube beyond the start point of the plate, which defines a reduced-gas fluid inlet port for the reduced-gas fluid flowpath. The internal tube interior opening preferably comprises a plurality of inlet perforations.
The gas-liquid separator further comprises a disk and an artificial lift assembly. The disk has a plurality of disk perforations extending through the disk and is positioned above the internal tube interior opening and below the internal annulus opening. The artificial lift assembly is positioned either above or below the plate. A second internal annulus opening is provided above the start point of the plate, which defines a free gas outlet port for the free gas flowpath. The second internal annulus opening preferably comprises a plurality of outlet perforations.
The plate of the liquid gas separator has a number of alternate configurations. In accordance with one configuration, the plate is a spiral plate which has at least one turn about the external tube. In accordance with another configuration, the plate is a first pitched plate which has at least a one-quarter turn about the external tube. A second pitched plate may also be provided which is aligned in parallel or in series with the first pitched plate.
An alternate gas-liquid separator of the present invention comprises the external and internal tubes as recited above and means for spinning a produced fluid mixture about the external tube. The spinning means is essentially static relative to the external tube.
The present invention is also a method for separating a gas from a fluid mixture down hole in a well bore. The method comprises producing a fluid mixture including a gas and a hydrocarbon liquid into a well bore from a point in a fluid production zone. An external tube with an external tube interior is positioned in the well bore and forms an external annulus between the external tube and a well bore face or casing. The fluid mixture is conveyed from the point in the fluid production zone through the external annulus to a flow channel at least partially encircling the external tube. The fluid mixture is then conveyed through the flow channel to spin the fluid mixture about the external tube. A portion of the gas is separated from the hydrocarbon liquid in the fluid mixture in response to spinning the fluid mixture, thereby producing a separated free gas and a reduced-gas fluid. The separated free gas is conveyed through a first opening in the external tube into the external tube interior and upward in the well bore via the external tube interior.
An internal tube having an internal tube interior is preferably positioned within the external tube interior to form an internal annulus in the external tube interior between the external tube and the internal tube and the separated free gas is conveyed upward in the well bore via the internal annulus. The separated free gas is subsequently conveyed through a second opening in the external tube from the external tube interior. The first opening in the external tube is preferably below the point in the fluid production zone and the second opening is preferably above the point in the fluid production zone. The reduced-gas fluid is conveyed through an opening in the internal tube into the internal tube interior and upward in the well bore via the internal tube interior. The second opening is above the first opening in the external tube and the first opening in the external tube is above the opening in the internal tube.
The present invention will be further understood from the drawings and the following detailed description.